1. Field of the Invention
The present invention relates to a vibratory flowmeter and method, and more particularly, to a meter electronics and fluid quantification method for a fluid being transferred.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flowmeters and vibrating densitometers, typically operate by detecting motion of a vibrating conduit that contains a flowing material. Properties associated with the material in the conduit, such as mass flow, density and the like, can be determined by processing measurement signals received from motion transducers associated with the conduit. The vibration modes of the vibrating material-filled system generally are affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.
A typical Coriolis mass flowmeter includes one or more conduits that are connected inline in a pipeline or other transport system and convey material, e.g., fluids, slurries, emulsions, and the like, in the system. Each conduit may be viewed as having a set of natural vibration modes, including for example, simple bending, torsional, radial, and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. Excitation is typically provided by an actuator, e.g., an electromechanical device, such as a voice coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow rate may be determined by measuring time delay or phase differences between motions at the transducer locations. Two such transducers (or pickoff sensors) are typically employed in order to measure a vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to electronic instrumentation. The instrumentation receives signals from the two pickoff sensors and processes the signals in order to derive a mass flow rate measurement, among other things. Vibratory flowmeters, including Coriolis mass flowmeters and densitometers, therefore employ one or more flow tubes that are vibrated in order to measure a fluid.
Bunkering refers to the practice of storing and transferring marine fuel oils, which have come to be known as bunker fuels. For ship fueling, large amounts of fuel may be temporarily stored in a barge or other container for the purpose of transferring fuel from shore to a ship. A bunker may be located on a dock or other port facility, or may be carried by a barge or other refueling vehicle. During bunkering, the fuel measurement usually comprises an empty-full-empty batching process, allowing gas to become entrained in the fuel.
Prior art fuel oil bunkering methods are based on volumetric tank measurements and a reference density typically obtained by laboratory sample. Look-up tables and reference density measurements are traditionally used to calculate the total mass of the delivered bunker fuel, in conjunction with a tank level measurement or dip tape measurement. Prior art measurement accuracy depends on many factors, including temperature, pressure, the presence or absence of entrained gas, dip tape measurement error or uncertainty, tank volume uncertainty, accuracy of conversion tables, human error, and how well the density sample represents the average batch density, for example. Further, heavy fuel oil (HFO) tends to stratify over time, so components may separate and have different densities, viscosities, etc.
While mass flow total is the most important measurement for a fuel transfer operation, the density and viscosity are also desired, as they are important indications of the quality or grade of the fuel oil. Generally, the higher the density and viscosity the lower the quality of fuel delivered. Knowledge of density and viscosity is essential for ensuring that the ideal fuel for a particular engine is used. In addition, a customer will want to determine how much of a fluid transfer is aerated. Such a determination can indicate whether the fuel is being intentionally aerated in order to increase the apparent volume of the fuel being delivered.
In the prior art, the current method for determining the bunker fuel's density and viscosity is to take a sample during the bunkering operation and send it to a laboratory for analysis. Unfortunately, laboratory analysis typically takes several days and the fuel will be on the ship and being used by that time. Further, fuel oil tends to stratify in tanks, leaving the lower grade fuel with the highest viscosity and density at the bottom of the tank and the higher quality fuel at the top. A single sample cannot capture the average density or viscosity of an entire batch.